Animal Nutrition

Animal Nutrition

Volume 13, June 2023, Pages 19-30
Animal Nutrition

Original Research Article
Total amino acid level affects the results of standardized ileal digestibility assays for feed ingredients for swine, rights and content
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open access


It has been demonstrated that the fiber content of oilseed meals and total amino acids (AA) in distillers' grains products affects standardized ileal digestibility (SID) values from swine assays and that total protein concentration affects the AA digestibility in assays using chickens. This analysis was conducted to test the hypothesis that the total AA content of test samples affects the SID assay results. Databases containing total AA profiles and SID values of 20 feedstuffs commonly fed to pigs from 2 sources, AMINODat 5.0 (Evonik Industries, 2015) and the Nutrient Requirements of Swine, 12th edition (NRC, 2012) were used to compare AA concentration effects on standardized ileal digestibility coefficients. Databases were compared with AA and SID available in both data sets. The total AA values were similar for the 2 databases with an R2 of 0.979 (P < 0.001). The linear relationship between digestibility coefficients from the 2 databases was highly significant, an R2 of 0.810 (P < 0.001). Both databases had increased SID values with increasing AA contents within and across feed ingredients. The SID = f(AA concentration) relationship was confirmed with an individual paper. Since SID, as typically measured, is a function of both digestion and absorption, both processes following Michaelis–Menten kinetics, SID = f(AA concentration) may simply be a natural phenomenon. Other reasons for the relationship were explored. Methods of estimating endogenous AA losses and misapplication statistical procedures may contribute to variation in results and at least partially explain why SID = f(AA concentration).


Apparent ileal digestibility
Standardized ileal digestibility
Least squares means

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Peer review under responsibility of Chinese Association of Animal Science and Veterinary Medicine.